DE-B-1100302 discloses an apparatus for measuring the diameter of workpieces coming out of a centreless grinding machine. The apparatus comprises a first conveying belt moving forward the workpieces, arranged on a guiding device, at a speed higher than that they have through the grinding machine, so that gaps arise between adjacent workpieces, a sliding guide receiving the workpieces from the first conveying belt, a retractable second conveying belt adapted to engage the workpieces under spring pressure for moving them on the sliding guide, a locking device for stopping the workpieces on the sliding guide, and a retractable measuring head for subsequently measuring the workpieces. The measurement of each workpiece is performed while the respective workpiece and other workpieces adjacent to it are stationary.
DE-B-1100302 also refers to a prior art apparatus in which the pieces to be checked are continuously moved, arranged in a row, past a contact type gauge.
It is known from U.S. Pat. No. 3,975,829 to carry out checkings--in particular dimensional checkings--of a plurality of pieces that have been machined by a machine tool. The pieces have a substantially cylindrical shape, and are arranged on a conveyor made of bars, the latter provide aligning and guiding in a determined direction, while a measuring head checks diametral dimensions of the pieces so aligned, during a translation displacement in said direction.
It is also known to carry out "non-destructive" tests of mechanical pieces to inspect the structural integrity after the machining by machine tools. These tests are of fundamental importance in mass production, in order to meet very strict specifications relating to the reliability and the safety of components subject to stresses.
In the specific case of rollers for bearings, it is important to check the presence of flaws or cracks, particularly on the rolling surfaces, that may appear during finishing operations carried out by honing machines like, for example, the one disclosed in German patent application DE-A-3707335.
In order to accomplish these checkings, there can be used "non-contact" probes, like eddy current probes, that scan the surface involved, by performing reciprocally combined translation and rotational displacements between probe and piece. More specifically, these reciprocal displacements can be achieved by causing, respectively, the roller to translate along the direction of its axis and a detection part of the probe to rotate, together with an associated annular support, about said axis.
As the surface defects of the pieces follow a casual statistical distribution, it is not sufficient to perform sample checkings, but it is necessary to inspect all the pieces. To this purpose, at the exit of the honing machine the rollers can be conveyed and guided in a row by a conveyor towards the detection probes, that rotate and scan the rotation surfaces of the pieces.
In the case of "barrel" shaped rollers, the carrying out of checking operations is difficult, due to problems in the positioning of the rollers. In fact, owing to the convex profile of their lateral surfaces, when the pieces are supported on a conveyor on relevant lateral surfaces they are subject to oscillations about transversal axes in consequence of the conveyor displacements, and the piece axes also oscillate and do not stand aligned along the feed direction. It is obvious that similar oscillations prejudice the possibility of detecting surface defects by means of detection probes.
On the other hand, the possible resting of the rollers on plane surfaces, with their associated axes lying in a perpendicular direction with respect to the conveyor feed direction, in a similar way to what is shown in U.S. Pat. No. 3,975,829 (considering pieces of a different type), makes it difficult, and in any case considerably complicated, to perform a check in series of the lateral surfaces of different pieces in the formerly briefly described manner.
U.S. Pat. No. 4,864,239 relates to an apparatus for inspecting cylindrical parts, such as roller bearings, by means of an eddy-current probe. A determined number of parts is loaded onto a cradle device including three rollers and spring loaded end stops that abut the neighboring parts into a stack.
The parts are made to rotate about a longitudinal axis by the rollers of the cradle device, while the eddy-current probe is displaced, step-wise or continuously, along the longitudinal direction.
U.S. Pat. No. 3,863,352 relates to a gauging device for measuring workpieces, such as rings, as they are discharged from a grinding machine.
The workpieces leaving the grinding machine move on guide means having a downward inclination and then enter into contact with a drive endless belt that displaces them at a determined speed toward a gauging station including a gauging device for measuring the thickness of the workpieces.